Methods and devices for controlling ablation therapy

ABSTRACT

Devices and methods for controlling ablation therapy are provided herein. In one embodiment, an ablation device is provided that includes an elongate body having proximal and distal ends, and an inner lumen extending therethrough. The inner lumen can be configured to receive fluid therein and to deliver fluid to the distal end of the elongate body. The device can also include an ablation element positioned at a distal end of the elongate body that is configured to heat surrounding tissue, and a heater element disposed within the inner lumen adjacent to a distal end of thereof, the heater element being configured to heat fluid flowing through the inner lumen.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/445,373, filed on Apr. 12, 2012, now issued as U.S. Pat. No.9,445,861 and entitled “Methods and Devices for Controlling AblationTherapy,” which claims priority to U.S. Provisional Application No.61/474,574, filed on Apr. 12, 2011, entitled “Ablation Catheters.” Thisapplication is also related to U.S. application Ser. No. 13/445,034,entitled “Devices and Methods for Remote Temperature Monitoring in FluidEnhanced Ablation Therapy,” U.S. application Ser. No. 13/445,036, nowissued as U.S. Pat. No. 9,138,287 and entitled “Methods and Devices forHeating Fluid in Fluid Enhanced Ablation Therapy,” U.S. application Ser.No. 13/445,040, now issued as U.S. Pat. No. 8,945,121 and entitled“Methods and Devices for Use of Degassed Fluids with Fluid EnhancedAblation Devices,” and U.S. application Ser. No. 13/445,365, now issuedas U.S. Pat. No. 8,702,697 and entitled “Devices and Methods for ShapingTherapy in Fluid Enhanced Ablation,” all of which were filedconcurrently with the present application. The disclosures of each ofthese applications are hereby incorporated by reference in theirentirety.

FIELD

The present application relates generally to the control of ablationtherapy. More particularly, this application relates to improved devicesand methods for controlling ablation therapy.

BACKGROUND

The use of thermal energy to destroy bodily tissue can be applied to avariety of therapeutic procedures, including the treatment of cardiacarrhythmias, such as atrial fibrillation. In such a procedure, thermalenergy can be imparted to the arrhythmogenic myocardium using variousforms of energy, such as radio frequency electrical energy, microwave orlight wave electromagnetic energy, or ultrasonic vibrational energy.Radio frequency (RF) ablation, for example, can be effected by placing acatheter within the heart and pressing an emitting electrode disposed onthe catheter against the heart wall near the region of the myocardiumthat is causing the arrhythmia. High frequency electrical current can bepassed into the tissue between closely spaced emitting electrodes orbetween the emitting electrode and a larger, common electrode locatedremotely from the tissue to be heated. The energy can heat themyocardium to a temperature that will cause necrosis (e.g., atemperature above about 50° C.).

One embodiment of a prior art ablation catheter is shown in FIG. 1. Thecatheter 100 includes a plurality of sensing electrodes 102 disposedthereon that are used to detect electrical activity in the heart. Themeasurement of electrical activity can be used to detect thearrhythmogenic tissue and guide the placement of the catheter. Thecatheter also includes a large electrode or other ablation element 104disposed on the distal end thereof that is effective to transmit RFelectrical energy into the myocardium 106. In use, the electrode 104 onthe distal tip of the catheter 100 is placed against the surface of themyocardium 106 in a desired location, and the electrode is subsequentlyactivated to heat the tissue.

Prior art ablation catheters have a number of disadvantages. Forexample, using the above techniques, maximum heating often occurs at ornear the interface between the catheter electrode 104 and the tissue106. In RF ablation, for example, maximum heating can occur in thetissue immediately adjacent to the emitting electrode. Furthermore, asthese techniques are increasingly used in areas having thicker tissuewalls, the RF power level must be increased to effect heating at greaterdepths within the tissue. This can result in even higher levels ofheating at the interface between the electrode and the tissue. Asdescribed in more detail below, these high levels of heating can reducethe conductivity of the tissue, effectively preventing the transmissionof further energy into the tissue. In addition, some levels of heatingcan produce dangerous medical complications for a patient, including,for example, clots that can result from overheating surrounding blood.

Accordingly, there is a need for improved methods and devices forcontrolling ablation therapy.

SUMMARY

The present invention generally provides devices and methods forcontrolling ablation therapy. In particular, the devices and methodsdescribed herein permit regulation of the temperature of an ablationelement being used to emit ablative energy into tissue. By controllingthe temperature of the ablation element, the undesirable effectsassociated with overheating the tissue can be avoided. This, in turn,can allow a greater amount of tissue to be treated using a lower amountof ablative energy, thereby reducing the risk of unintended damage totissue.

In one aspect, an ablation device is provided that includes an elongatebody having proximal and distal ends, and an inner lumen extendingtherethrough. The device further includes an ablation element positionedat the distal end of the elongate body, the ablation element beingconfigured to heat surrounding tissue. The inner lumen of the elongatebody is configured to receive fluid therein such that the fluid flows tothe distal end of the elongate body. The device further includes aheater element disposed within the inner lumen adjacent to a distal endthereof. The heater element can be configured to heat fluid flowingthrough the inner lumen.

The devices and methods described herein can have a variety ofmodifications and additional features, all of which are consideredwithin the scope of the invention. For example, in some embodiments theelongate body and the ablation element can be non-porous such that fluidis preventing from flowing therethrough. The inner lumen can include adelivery lumen, as well as a return lumen such that fluid can flowdistally through the delivery lumen to the distal end, and then flowproximally through the return lumen to the proximal end of the elongatebody. In other embodiments, the elongate body can include one or moreoutlet ports formed through a sidewall thereof adjacent to the distalend thereof, the outlet ports being configured to allow fluid to flowfrom the inner lumen and into surrounding tissue.

In certain embodiments, the device can further include a temperaturesensor disposed on a distal end of the ablation element to sample atemperature at the interface between the ablation element and a tissuewall. In certain embodiments, the temperature sensor can be recessedwithin the ablation element such that it does not protrude from a distalend thereof. In other embodiments still, the temperature sensor can bedisposed within the inner lumen of the elongate body and in contact withthe ablation element.

In some embodiments, the device can include a different temperaturesensor positioned adjacent to the distal end of the inner lumen at alocation distal to the heater element in order to sample a temperatureof fluid heated by the heater element. Still further, in someembodiments the device can include a temperature sensor positionedproximal to the heater element within the inner lumen to sample thetemperature of fluid flowing through the inner lumen.

The heater element can have a variety of forms. In some embodiments, theheater element can include at least one wire extending through the innerlumen and configured to pass Radio Frequency (RF) electrical energythrough fluid flowing through the inner lumen. In other embodiments, theheater element can be a resistive element disposed within the innerlumen.

The ablation element can, in some embodiments, form a blunt distal tipof the elongate body that is configured to contact tissue withoutpenetrating through the tissue. In other embodiments, however, theablation element can have a variety of other shapes.

In another aspect, a method of ablating tissue is provided that includespositioning a blunt distal portion of an elongate body in contact withtissue, and delivering ablative energy to the tissue through an ablationelement while simultaneously delivering fluid through the elongate bodywhere the fluid is heated by a heater element disposed in a distalportion of the elongate body. The fluid can be heated to control theablation therapy provided to the tissue by the ablation element.

In some embodiments, the blunt distal portion of the elongate body doesnot penetrate the tissue when positioned in contact therewith, butrather abuts against a surface of the tissue. In other embodiments, theablation element is positioned at that distal end of the elongate body,such that the distal end of the elongate body is positioned in contactwith tissue.

In other embodiments, delivering fluid through the elongate body caninclude forcing fluid through an inner lumen disposed within theelongate body. In certain embodiments, the heater element can bedisposed within the inner lumen. In still other embodiments, the methodcan further include receiving fluid delivered through the elongate bodyat a proximal end thereof, e.g., such that the fluid circulates throughthe elongate body without exiting at the distal end of the elongatebody. In some embodiments, however, the fluid delivered through theelongate body can flow through one or more outlet ports formed in theablation element into the surrounding tissue or fluid.

In certain embodiments, the method can further include detecting atemperature of the tissue in contact with the blunt distal portion ofthe elongate body using a temperature sensor disposed on a distal end ofthe elongate body. In other embodiments, however, the method can includedetecting the temperature of the fluid delivered through the elongatebody using a temperature sensor disposed distal to the heater element.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects and embodiments of the invention described above will bemore fully understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of one embodiment of a prior art ablation device;

FIG. 2 is a chart showing a temperature profile created in tissue by theprior art ablation device of FIG. 1;

FIG. 3 is a chart showing a temperature profile created in tissue by aprior art ablation device cooled by unheated fluid;

FIG. 4 is a chart showing a temperature profile created in tissue by thedevice of FIG. 3 following an increase in ablative energy level;

FIG. 5 is a chart showing a temperature profile created in tissue usingone embodiment of an ablation device of the present invention;

FIG. 6 is a side view of one embodiment of an ablation device having aclosed loop flow pattern; and

FIG. 7 is a side view of one embodiment of an ablation device having anopen loop flow pattern.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the devices and methodsdisclosed herein. One or more examples of these embodiments areillustrated in the accompanying drawings. Those skilled in the art willunderstand that the devices and methods specifically described hereinand illustrated in the accompanying drawings are non-limiting exemplaryembodiments and that the scope of the present invention is definedsolely by the claims. The features illustrated or described inconnection with one exemplary embodiment may be combined with thefeatures of other embodiments. Such modifications and variations areintended to be included within the scope of the present invention.

The terms “a” and “an” can be used interchangeably, and are equivalentto the phrase “one or more” as utilized in the present application. Theterms “comprising,” “having,” “including,” and “containing” are to beconstrued as open-ended terms (i.e., meaning “including, but not limitedto,”) unless otherwise noted. The terms “about” and “approximately” usedfor any numerical values or ranges indicate a suitable dimensionaltolerance that allows the composition, part, or collection of elementsto function for its intended purpose as described herein. These termsgenerally indicate a ±10% variation about a central value. Componentsdescribed herein as being coupled may be directly coupled, or they maybe indirectly coupled via one or more intermediate components. Therecitation of any ranges of values herein is merely intended to serve asa shorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited. All methods described herein can be performed inany suitable order unless otherwise indicated herein or otherwiseclearly contradicted by context. The use of any and all examples, orexemplary language (e.g., “such as”), provided herein is intended merelyto better illuminate the invention and does not impose a limitation onthe scope of the invention unless otherwise claimed. No language in thespecification should be construed as indicating any non-claimed elementas essential to the practice of the invention. Further, to the extentthe term “saline” is used in conjunction with any embodiment herein,such embodiment is not limited to the use of “saline” as opposed toanother fluid unless explicitly indicated. Other fluids can typically beused in a similar manner.

As described above, conventional ablation techniques using a devicesimilar to the ablation catheter 100 of FIG. 1 can produce maximalheating of tissue at the interface between the ablation element, such aselectrode 104, and the tissue, such as myocardium 106. Use of such adevice can produce the temperature profile 200 of FIG. 2 thatillustrates the temperature (in degrees Celsius) as a function of thedepth (in millimeters) from the tissue surface. As shown in the figure,the ablation catheter 100 can create a therapeutically treated lesion intissue that is 1 mm deep. That is, the depth to which the tissue isheated above 50° C. is 1 mm. A temperature of 50° C. is used herein asan example of a threshold for determining when a particular volume oftissue has been therapeutically treated, i.e., has received a thermaldose sufficient to cause necrosis within the volume (see Nath, S. andHaines, D. E., Prog. Card. Dis. 37(4):185-205 (1995) (Nath et al.)).However, this number is provided by way of example only, as theliterature contains a number of different methodologies for determiningthermal dose administration, any of which can be utilized with themethods and devices of the present invention.

Referring back to FIG. 2, the shallow treatment depth produced by theprior art ablation catheter 100 is often only effective for use withsuperficial arrhythmogenic tissue or, for example, in regions of theheart where the wall is very thin (e.g., thin atrial walls). As the useof ablation in the treatment of atrial fibrillation and other cardiacconditions has increased over time, ablation therapy has been used inareas having much thicker tissue walls. One method for increasing thedepth to which an ablation catheter can heat is to cool the surface ofthe ablation element, e.g., the electrode 104. To accomplish this, afluid can be pumped down the ablation catheter to contact the ablationelement disposed adjacent to the distal end of the catheter. In somecases, the fluid can contact a rear surface of the ablation element andreturn up the catheter body. In other cases, however, the fluid can flowout of the ablation catheter through one or more ports or pores formedin the ablation element itself.

In either case, fluid (e.g., saline) can be introduced into the ablationcatheter at room temperature and is often heated to near bodytemperature by the surrounding blood as the fluid moves through the bodytoward the distal end of the catheter. The flowing body-temperaturefluid can cool and constrain the ablation element to a temperature thatis about body temperature, or 37° C.

An exemplary temperature profile created by such a device is shown inFIG. 3. As the profile 300 illustrates, contacting the ablation elementwith body-temperature fluid can be effective to reduce the heating thatoccurs at the interface between the ablation element and the tissuewall. However, the cooling can also be effective to reduce the entireheating field to such a degree that the effectiveness of the ablationtherapy is reduced, i.e., only a very small portion of tissue is heatedabove the desired therapeutic temperature of 50° C. This same effect canalso be seen in areas of the heart (or other organs) where blood vesselsor arteries produce effective localized cooling by moving blood past thetreatment site. For example, in atrial fibrillation it can be necessaryto perform ablation near the coronary sinus, and the large amount ofblood flow in this area can effectively cool the heating fields createdby any ablation devices.

To compensate for this cooling effect, the level of RF power used toheat the tissue can be increased. An increase in RF power in combinationwith fluid cooling of the ablation element can, for example, produce thetemperature profile 400 shown in FIG. 4. The increase in power can havethe positive effect of increasing the depth of therapeutic treatment(e.g., the depth of therapeutic treatment increases to 2 mm), but comesat the cost of producing a higher maximum temperature within the tissue.Furthermore, the position of the maximum temperature can be shifted intothe tissue as a result of the cooling of the ablation element. Becausethis maximum temperature can no longer be directly observed due to itsposition at depth, it can be difficult to control the balance betweenthe amount of RF heating and the amount of cooling provided by thefluid. In such a situation, temperatures within the tissue can exceed100° C. in some locations, as shown in FIG. 4. Exceeding 100° C. canproduce a number of undesirable effects. For example, above 100° C.tissue can desiccate, or dry up, and overheat. This can produce charringand lead to an increase in the impedance of the tissue. As the impedanceincreases, the amount of electrical energy that can pass through thetissue decreases. Accordingly, impedance rises can effectively stop anyfurther ablation therapy since energy is no longer transferred deeperinto the tissue. Still further, such high temperatures can also causesuperheating of any fluid in the tissue. In some cases, impedancepops—or the explosive phase change of superheated fluid to steam—canoccur. These small explosions can cause damage in the tissue wall andpotentially lead to serious medical complications (e.g., perforations inthe heart wall, etc.).

To address these issues, methods and devices are provided herein tocontrol the temperature and power level of an ablation element tothereby prevent undesirable temperature spikes while maintaining thedepth of the treatment lesion created during ablation therapy. FIG. 5illustrates an exemplary temperature profile 500 that can be achievedusing the methods and devices described herein. In one embodiment, aheating element can be implemented in an ablation device to deliverfluid at a controlled and desired temperature to cool an ablationelement. The temperature of the fluid can be selected such that theablation element is cooled to a temperature below about 100° C. Morepreferably, the fluid can be cooled to a temperature between about 20°C. and 100° C. Still more preferably, the fluid can be cooled to atemperature between about 37° C. and 100° C.

For example, and as shown in the figure, the ablation element can becooled to a temperature of about 60° C. Regulating the temperature ofthe ablation element to this level can prevent the desiccation andimpedance rise associated with heating above 100° C., but can also allowfor deeper therapeutic heating using a lower RF power level. Forexample, the profile 500 shows that tissue to a depth of 5 mm can beheated above 50° C. with no tissue rising above about 80° C. While 60°C. is illustrated as an example, any temperature between about 37° C.and 100° C. can be selected. For example, a temperature of 40, 50, 60,70, 80, or 90° C. can be selected. The selection of the fluidtemperature (which can approximate the ablation element temperaturebecause the flowing fluid can cool the ablation element to approximatelythe same temperature) and RF power level can be coordinated such that atreatment lesion of a desired depth is created without heating anyportion of the tissue above about 100° C.

A number of different devices and methods can be employed to heat thecooling fluid to a desired temperature. FIG. 6 illustrates oneembodiment of an ablation device 600. The device 600 includes anelongate body, which can be rigid or flexible and can be formed from avariety of biocompatible materials. For example, the elongate body 602can be a flexible catheter body, or can be a rigid body disposed at adistal end of a catheter used to introduce the elongate body 602 to atreatment site. The elongate body 602 can also include an inner lumen604 extending therethrough that can be configured to provide a passagefor fluid flow through the elongate body. Further, the particular sizeof the elongate body can depend on a variety of factors including thetype and location of tissue to be treated, etc. By way of example only,in one embodiment, a very small elongate body can be utilized to accessthe heart of a patient. In such an embodiment, an appropriately sizedelongate body can be, for example, a catheter having a diameter of about8 French (“French” is a unit of measure used in the catheter industry todescribe the size of a catheter and is equal to three times the diameterof the catheter in millimeters). The elongate body can be formed from aconductive material such that the elongate body can conduct electricalenergy along its length to an ablation element disposed thereon.Alternatively, the elongate body can be formed from, or coated in, aninsulating material and any electrical communication between anycomponents coupled thereto can be accomplished through electricalconnections running along or within the elongate body.

The elongate body 602 can also include an ablation element 606 disposedalong a length thereof adjacent to its distal end. As shown in thefigure, in some embodiments the ablation element 606 can be positionedat the distal end of the elongate body 602. The ablation element 606 canbe formed from a variety of materials suitable for conducting current.Any metal or metal salt may be used. Aside from stainless steel,exemplary metals include platinum, gold, or silver, and exemplary metalsalts include silver/silver chloride. In one embodiment, the electrodecan be formed from silver/silver chloride. It is known that metalelectrodes assume a voltage potential different from that of surroundingtissue and/or liquid. Passing a current through this voltage differencecan result in energy dissipation at the electrode/tissue interface,which can exacerbate excessive heating of the tissue near theelectrodes. One advantage of using a metal salt such as silver/silverchloride is that it has a high exchange current density. As a result, alarge amount of current can be passed through such an electrode intotissue with only a small voltage drop, thereby minimizing energydissipation at this interface. Thus, an electrode formed from a metalsalt such as silver/silver chloride can reduce excessive energygeneration at the tissue interface and thereby produce a more desirabletherapeutic temperature profile, even where there is no liquid flowabout the electrode.

In some embodiments, the ablation element 606 can be disposed at adistal end of the elongate body 602. The ablation element 606 can have avariety of shapes but, in some embodiments, can be shaped to form ablunt distal tip of the device 600. As such, the ablation element 606can be configured to press against, or be positioned adjacent to, atissue wall without penetrating into the tissue wall. Furthermore, theablation element 606 can be formed from a non-porous material or, insome embodiments, the ablation element 606 can have one or more outletports or pores formed therein that provide fluid communication betweenthe inner lumen and the tissue and/or fluids surrounding the ablationelement.

In some embodiments, the inner lumen of the elongate body 602 caninclude a delivery lumen 608 configured to provide a passage for fluidflow from the proximal end to the distal end, and a return lumen formedby the annular space between the delivery lumen 608 and the inner wallof the inner lumen 604. The return lumen can be configured to receivefluid at a distal end thereof and deliver the fluid back to the proximalend of the elongate body 602. This allows fluid to be circulated throughthe elongate body without the need to release the fluid to thesurrounding tissue. Similar to the elongate body 602, the delivery lumen608 can be formed from a variety of materials that are rigid, flexible,polymeric, metallic, conductive, or insulating. Further, the deliverylumen 608 can be positioned within the inner lumen 604 of the elongatebody 602 such that the delivery lumen does not move with respect to theelongate body, or can be allowed to float freely within the elongatebody 602. In some embodiments, the delivery lumen 608 can be a hollowtube disposed within the inner lumen of the elongate body. In addition,in certain embodiments, the return lumen can be a separate hollow tubedisposed within the inner lumen 604 of the elongate body.

In some embodiments, the delivery lumen 608 can house a heating assemblyor heater element 612 disposed adjacent to a distal end of the deliverylumen and configured to heat fluid flowing through the delivery lumen.The heating assembly 612 can be connected to a power supply andcontroller coupled to the proximal end of the elongate body 602. Anumber of heating assemblies can be utilized to heat fluid flowingthrough the delivery lumen 608, including those described in U.S. Pat.No. 6,328,735 to Curley et al., and U.S. patent application Ser. No.13/445,036, entitled “Methods and Devices for Heating Fluid in FluidEnhanced Ablation Therapy,” filed concurrently herewith. The disclosuresof each of these references are hereby incorporated by reference intheir entirety. For example, the heater element 612 can be a resistivecoil disposed within the delivery lumen 608. In other embodiments,however, a heating assembly 612 formed from one or more wires suspendedin the delivery lumen 608 that can be used to pass RF electrical energythrough the fluid flowing through the delivery lumen, thereby heatingthe fluid due to its inherent electrical resistivity.

In certain embodiments, the delivery lumen 608 can also house atemperature sensor 614 configured to detect the temperature of the fluidflowing through the delivery lumen 608 after it is heated by the heatingassembly 612. For this reason, the temperature sensor 614 can, in someembodiments, be positioned distal to the heating assembly 612, and canbe separated from the heating assembly by a distance sufficient to allowmixing of the fluid after passing through the heating assembly (e.g.,about 1 mm). The temperature sensor 614 can have a variety of forms and,in some embodiments, can be a fine-wire thermocouple. The temperaturesensor 614 can be connected to a controller that can utilize thedetected fluid temperature to regulate the heating assembly 612.

In use, a fluid (e.g., saline) can be pumped through the delivery lumen608 from a proximal end thereof to a distal end that is positionedadjacent to the ablation element 606. The fluid can pass by the heatingassembly 612 and be heated to a desired temperature, e.g., anytemperature below 100° C., or any temperature between about 40 and about90° C., or between about 50 and about 80° C., or between about 60 andabout 70° C. In some embodiments, an additional temperature sensor (notshown) can be positioned in the delivery lumen 608 at a positionproximal to the heating assembly 612 in order to determine the initialtemperature of the fluid flowing through the delivery lumen 608 (andthereby determine a power output needed for the heating assembly 612).After being heated by the heating assembly 612, the fluid can mix andexit the delivery lumen 608 near the distal end of the elongate body 602adjacent to the ablation element 606. As shown by the flow directionarrows 616, the fluid can contact an inner surface of the ablationelement and subsequently be directed back toward the proximal end of theelongate body 602 through the return lumen. The movement of the fluidcan convect heat away from the ablation element 606, thereby regulatingits temperature. Given a sufficient flow rate, the ablation element 606can be regulated to about the same temperature of the fluid exiting thedelivery lumen 608.

In order to confirm the effectiveness of the temperature regulation, thedevice 600 can also include an external temperature sensor 618 disposedon a distal end of the device 600. In some embodiments, the temperaturesensor 618 can be recessed within the ablation element 606 such that itdoes not protrude from a distal end thereof. In still other embodimentsin which the ablation element 606 is formed from a metal or otherthermally conductive material, the temperature sensor 618 can bepositioned inside the inner lumen 604 touching a proximal surface of theablation element 606. Regardless of its position, the temperature sensor618 can be configured to detect the temperature at the interface betweenthe ablation element 606 and a tissue surface 620. Detecting thetemperature at this location can confirm that the ablation element 606is being cooled to the temperature of the fluid flowing from thedelivery lumen 608.

FIG. 7 illustrates another embodiment of an ablation device having anopen-loop flow, as opposed to the closed-loop flow shown in FIG. 6. Asshown in the figure, the device 700 can include several componentscommon to the device of FIG. 6. For example, the device 700 can includean elongate body 602 having an inner lumen 604, a delivery lumen 608disposed within the inner lumen 604 and having its own inner lumen 610,a heating assembly 612 and temperature sensor 614 housed within theinner lumen 610, and, in some embodiments, one or more additionaltemperature sensors, such as the temperature sensor 618.

The device 700 differs from the device 600 in that it includes anablation element 702 having a plurality of outlet ports or pores formedtherein that communicate between an inner surface and an outer surfaceof the ablation element. As a result, when fluid is introduced into theinner lumen 604 adjacent to the ablation element 702, the fluid can flowthrough the ablation element 702 and into the body cavity surroundingthe device 700. The resulting open-loop flow pattern is illustrated byflow direction arrows 704. As a result of the open-loop flow pattern,the device 700 can, in some embodiments, remove the separate deliverylumen 608 and simply pump fluid in a single direction through the innerlumen 604 of the elongate body 602. In such an embodiment, the heatingassembly and any temperature sensors can be disposed within the innerlumen 604 of the elongate body 602.

The devices shown in FIGS. 6 and 7 can both be used to administerablation therapy that prevents the overheating of tissue while producingtherapeutic treatment at greater depths than previously possible. Insome embodiments, however, it can be preferable to utilize theclosed-loop device 600 rather than the open-loop device 700. Forexample, in embodiments where the temperature of the fluid introducedfrom the delivery lumen 608 is sufficiently high (e.g., 70° C. andabove), it can be undesirable to allow the fluid to flow into thebloodstream or tissue surrounding the ablation device. Fluid at thattemperature can, in some cases, damage tissue or cause blood clots toform. Accordingly, it can be desirable to collect the heated fluid atthe proximal end of the device, rather than introduce the fluid into thepatient's body. This can vary by location and specific anatomy of thetreatment site, however. For example, areas having high blood flow maybe able to dissipate the high temperature fluid without risk ofdeveloping complications.

The devices described above can be utilized in a variety of proceduresrequiring ablation of tissue within the body. For example, the devicesand methods disclosed herein can be particularly useful in cardiacablation. Procedures for the treatment of atrial fibrillation and atrialflutter, such as the Maze Procedure, often require ablating a largeamount of the cardiac anatomy in locations where the tissue walls havevariable thickness. The methods and devices of the present inventionallow operators to ablate a variety of tissue geometries using a minimumlevel of RF power and without overheating tissue at any depth.

For example, in ablating a thicker wall of the myocardium, a devicesimilar to the device 600 can be inserted into a patient's body via anaccess port or other opening formed through one or more layers oftissue, or via a natural orifice (i.e., endoscopically). The device cansubsequently be delivered to any treatment site within the bodydirectly, or using existing passageways within the body (e.g., passingthe device into the heart through a patient's blood vessels). Once inthe vicinity of a desired treatment site, the ablation element of thedevice can be positioned using the aid of sensing electrodes or otherpositioning instruments, and the distal tip of the ablation element canbe pressed against a tissue wall at a particular location. Further, inmany embodiments the elongate body and/or ablation element can have ablunt distal end, such that the elongate body and/or ablation elementcan be pressed against a tissue wall without penetrating through thetissue. Following positioning, RF energy can be delivered into thetissue wall while fluid is simultaneously delivered through the elongatebody, e.g., through a delivery lumen. The fluid can be heated by aheating assembly positioned in a distal portion of the elongate body,e.g., within a distal portion of the delivery lumen. The fluid cancontact the ablation element and either flow through ports formed in theablation element or flow back up to the proximal end of the elongatemember to convect heat away from the ablation element. The delivery ofthe heated fluid can effectively regulate the temperature of theablation element to match that of the heated fluid. The controlled andelevated operating temperature can allow ablation therapy to beconducted using an efficient level of RF power, and the heating oftissue above a threshold level, e.g., 100° C., can be avoided.

The above exemplary embodiments describe the treatment of cardiactissue. While this is one contemplated use, the methods and devices ofthe present invention can be equally adapted for use in other areas of apatient's body. As such, the devices described herein can be formed in avariety of sizes and materials appropriate for use in various areas of apatient's body.

In addition, those that are knowledgeable in the art will recognize thatthe heating mechanism for producing hyperthermia within the targettissue sufficient to destroy it can include other forms of energy.Ultrasonic vibrational energy is known to be absorbed by tissue andconverted to heat, as is microwave and light wave electromagneticenergy. Alternative embodiments may employ ultrasonic transducers,microwave antennas, or light wave diffusers as emitters disposed in thedistal end of an elongate body. Light wave electromagnetic energy canfall in a range spanning visible, near-infrared, infrared, andfar-infrared radiation, and can be generated by filaments, arc lamps,lasers of various forms (e.g., diodes, semiconductors, or pumps), or byother means. Similarly, the heating assembly or element described abovecan have a variety of forms, including a resistive wire for heating thefluid through conduction. Regardless of the type of ablation elementutilized, the injection of heated liquid into the elongate body adjacentto the ablation element can aid in regulating its temperature, and usingsaline heated above room temperature can increase the efficiency of theablation therapy and allow the use of lower RF power. It is alsorecognized that the devices described above can be delivered to atreatment site using any standard medical delivery device, depending onthe tissue to be treated. Exemplary alternative embodiments can includemetallic or nonmetallic needle bodies, sheaths, or introducers.

The devices disclosed herein can be designed to be disposed after asingle use, or they can be designed for multiple uses. In either case,however, the device can be reconditioned for reuse after at least oneuse. Reconditioning can include any combination of the steps ofdisassembly of the device, followed by cleaning or replacement ofparticular pieces, and subsequent reassembly. In particular, the devicecan be disassembled, and any number of the particular pieces or parts ofthe device can be selectively replaced or removed in any combination.Upon cleaning and/or replacement of particular parts, the device can bereassembled for subsequent use either at a reconditioning facility or bya surgical team immediately prior to a surgical procedure. Those skilledin the art will appreciate that reconditioning of a device can utilize avariety of techniques for disassembly, cleaning/replacement, andreassembly. Use of such techniques, and the resulting reconditioneddevice, are all within the scope of the present invention.

For example, the devices disclosed herein may be disassembled partiallyor completely. In particular, the elongate body 602 of the medicaldevice 600 shown in FIG. 6 may be decoupled from any control handle orother connected component, or the elongate body 602 can be separatedfrom the ablation element and/or any delivery lumen extendingtherethrough. Similarly, the heating assembly or element 612 and thetemperature sensor 614 can be separated from the delivery lumen 608and/or elongate body 602 for cleaning and/or replacement. These areexemplary disassembly steps only, as any component of the device can beconfigured to separate from the device for cleaning and/or replacement.

Preferably, the devices described herein will be processed beforesurgery. First, a new or used instrument can be obtained and, ifnecessary, cleaned. The instrument can then be sterilized. In onesterilization technique, the instrument is placed in a closed and sealedcontainer, such as a plastic or TYVEK bag. The container and itscontents can then be placed in a field of radiation that can penetratethe container, such as gamma radiation, x-rays, or high-energyelectrons. The radiation can kill bacteria on the instrument and in thecontainer. The sterilized instrument can then be stored in the sterilecontainer. The sealed container can keep the instrument sterile until itis opened in the medical facility.

In many embodiments, it is preferred that the device is sterilized. Thiscan be done by any number of ways known to those skilled in the artincluding beta or gamma radiation, ethylene oxide, steam, and a liquidbath (e.g., cold soak). In certain embodiments, the materials selectedfor use in forming components such as the elongate body may not be ableto withstand certain forms of sterilization, such as gamma radiation. Insuch a case, suitable alternative forms of sterilization can be used,such as ethylene oxide.

All papers and publications cited herein are hereby incorporated byreference in their entirety. One skilled in the art will appreciatefurther features and advantages of the invention based on theabove-described embodiments. Accordingly, the invention is not to belimited by what has been particularly shown and described, except asindicated by the appended claims.

The invention claimed is:
 1. A method of ablating tissue, comprising:positioning a blunt distal portion of an elongate body in contact withtissue; delivering ablative energy to the tissue through an ablationelement on the blunt distal portion of the elongate body; deliveringfluid from a proximal end to a distal end of the elongate body through adelivery lumen within an inner lumen of the elongate body; returningfluid from the distal end to the proximal end of the elongate bodythrough a return lumen within the inner lumen of the elongate bodywithout releasing the fluid into tissue; heating the fluid to atemperature greater than 37° C. and less than 100° C. using a heaterelement disposed in a distal portion of the elongate body; whereinheating the fluid using a heater element includes passing electricalcurrent through at least one wire that extends through at least onespacer to pass energy through fluid flowing through the inner lumen ofthe elongate body; wherein the at least one spacer is configured tomaintain a position of the at least one wire within he inner lumen ofthe elongate body, and wherein heating the fluid using a heater elementincludes passing electrical current from a first power source between asingle wire and a conductive elongate body.
 2. The method of claim 1,wherein the blunt distal portion of the elongate body does not penetratethe tissue.
 3. The method of claim 1, wherein the ablation element ispositioned at the distal end of the elongate body and adjacent to thetissue.
 4. The method of claim 1, wherein the heater element is disposedwithin the inner lumen to heat the fluid.
 5. The method of claim 1,further comprising detecting the temperature of the tissue in contactwith the blunt distal portion of the elongate body using a temperaturesensor disposed on a distal end of the elongate body.
 6. The method ofclaim 1, further comprising detecting the temperature of the fluiddelivered through the elongate body using a temperature sensor disposeddistal to the heater element.
 7. The method of claim 6, furthercomprising adjusting an output level of any of the ablation element andthe heater element to maintain the temperature of the ablation elementabove 37° C. and below 100° C.
 8. The method of claim 1, whereindelivering ablative energy to the tissue through an ablation elementincludes passing electrical current from a second power source betweenthe conductive elongate body and a collector electrode positionedoutside the inner lumen.
 9. The method of claim 1, wherein the returnlumen is defined by the annular space between the delivery lumen and aninner wall of the elongate body inner lumen.
 10. The method of claim 1,wherein the delivery lumen and the return lumen are each separate hollowtubes disposed within the inner lumen of the elongate body.
 11. Themethod of claim 1, wherein the delivery lumen is positioned within theinner lumen of the elongate body such that it does not move with respectto the elongate body.
 12. The method of claim 1, wherein the deliverylumen floats freely within the inner lumen of the elongate body.
 13. Amethod of ablating tissue, comprising: positioning a blunt distalportion of an elongate body in contact with tissue; delivering ablativeenergy to the tissue through an ablation element on the blunt distalportion of the elongate body; delivering fluid from a proximal end to adistal end of the elongate body through a delivery lumen within an innerlumen of the elongate body; returning fluid from the distal end to theproximal end of the elongate body through a return lumen within theinner lumen of the elongate body without releasing the fluid intotissue; heating the fluid to a temperature greater than 37° C. and lessthan 100° C. using a heater element disposed in a distal portion of theelongate body; wherein heating the fluid using a heater element includespassing electrical current through at least one wire that extendsthrough at least one spacer to pass energy through fluid flowing throughthe inner lumen of the elongate body; wherein the at least one spacer isconfigured to maintain a position of the at least one wire within theinner lumen of the elongate body; and wherein heating the fluid using aheater element includes passing electrical current through two wiresthat extend through two spacers.
 14. The method of claim 13, wherein theblunt distal portion of the elongate body does not penetrate the tissue.15. The method of claim 13, wherein the ablation element is positionedat the distal end of the elongate body and adjacent to the tissue. 16.The method of claim 13, further comprising detecting the temperature ofthe tissue in contact with the blunt distal portion of the elongate bodyusing a temperature sensor disposed on a distal end of the elongatebody.
 17. The method of claim 13, further comprising detecting thetemperature of the fluid delivered through the elongate body using atemperature sensor disposed distal to the heater element.
 18. The methodof claim 17, further comprising adjusting an output level of any of theablation element and the heater element to maintain the temperature ofthe ablation element above 37° C. and below 100° C.
 19. The method ofclaim 13, wherein the return lumen is defined by the annular spacebetween the delivery lumen and an inner wall of the elongate body innerlumen.
 20. The method of claim 13, wherein the delivery lumen and thereturn lumen are each separate hollow tubes disposed within the innerlumen of the elongate body.
 21. The method of claim 13, wherein thedelivery lumen is positioned within the inner lumen of the elongate bodysuch that it does not move with respect to the elongate body.
 22. Themethod of claim 13, wherein the delivery lumen floats freely within theinner lumen of the elongate body.